IAP2-23-017

Understanding water security and multi-hazards in volcanic Islands: a case of Tristan da Cunha

Rationale:
Small islands, whether islands within a larger state or Small Island Developing States (SIDS), are recognised as a ‘special case’ by the United Nations Disaster Risk Reduction Global Assessment Report on Disaster Risk Reduction in view of their unique characteristics and intrinsic vulnerabilities to environmental and economic shocks. They are often multi-hazard environments, with flora and fauna at risk from the impacts of complex hazard interrelationships, not least the existential threat of climate change, to which they are disproportionally vulnerable.

Many small islands are underlain by volcanic aquifers which are central to community water security. Reliance on volcanic aquifers in small islands is likely to increase as rainfall and surface water sources become more variable and less predictable with climate change. Yet volcanic aquifers remain poorly understood, in part due to their complexity and lack of accessibility. Furthermore, in these multi-hazard environments, water – either too much or too little – can trigger or amplify disasters, for example, resulting in flooding, landslides and drought.

Studying multi-hazard processes and environments can be extremely challenging and often requires multi and interdisciplinary approaches for knowledge development. However small islands can offer a well-bounded case study setting to simultaneously explore discrete physical and social processes within a holistic research framework.

Case Study: Tristan da Cunha
Tristan da Cunha, hereafter referred to as Tristan, is a remote active volcanic island in the South Atlantic Ocean. It is an extreme environment in many ways – a 12 km diameter, 2060 m high rock with no mainland neighbours for nearly 3000 km; on the edge of the Roaring Forties so punished by cold Antarctic winds and turbulent seas; an active, unmonitored volcano in a tectonically and volcanically active region (last subaerial eruption was 1961/62, last nearby submarine eruption was 2004); highly prone to mass movements, heavy rainfall, flooding and coastal erosion, and huge challenges of accessibility with only monthly ship visits (no airstrip).

The problem:
If that wasn’t enough, despite being a fascinating multi-hazard case study, Tristan is a data-poor environment. Although recent studies have developed knowledge on the eruptive history and geomorphological evolution of the island, what data we do have point to complexities in eruptive behaviour, diversity in eruptive composition, morphology, and future vent location. A landslide mapping and modelling study conducted last year also assessed the impact of recent mass movement and points to the need for longitudinal studies and monitoring for risk reduction. Yet the most pressing knowledge gap to address, and one linked to many of Tristan’s multi-hazards, is that of the hydrology and hydrogeology. An estimated 5000 mm of rain falls annually on the summit, but runoff pathways and storage rates are largely unknown.

Why Tristan?
Why then, do we want to conduct research on the most remote populated island in the world? 1) Tristan is one of 14 British Overseas Territories with a permanent member of the Foreign, Commonwealth and Development Office residing on-island. This facilitates collaboration with decision makers and more direct routes for provision of evidence to support decision making; 2) Tristan’s relatively small size makes for working in a well-bounded, natural laboratory with untold opportunities for novel single, multi and interdisciplinary research; 3) it is niche in terms of human geography too – Tristan is home to 235 islanders (Tristanians) which makes it a ‘goldilocks’ population for social scientific sampling; 4) to date, scientific research on Tristan has largely been focused on terrestrial biodiversity and marine conservation (a marine protection zone was declared in 2020 making 700,000km2 of water around Tristan the largest no-take zone in the Atlantic). There is therefore tremendous opportunity to collaborate with large conservation programmes; 5) volcanic environments are complex groundwater systems, Tristan presents a unique opportunity to better understand the hydrogeology of these systems, their vulnerabilities including the role of tectonic and volcanic activity, and how climate change might affect future water security of the community.

Stories of Resilience:
Tristanians are the first responders to any disaster on-island or in nearby waters. Due to the time it takes to mobilise external support, response to the impacts of natural hazards is usually managed without it. In part due to their remoteness and strong social capital, the population have developed resilience – even to extreme events – during their 200 years of habitation. However, dynamic environments and changing circumstances are threatening this resilience. Impacts from geohazards in the last five years, particularly flooding and landslides in 2016 and 2017, have been the most severe of their kind to affect the islanders in recorded history (apart from the 1961-62 eruption of the volcano). The impacts from flooding and landslides have, at times, overwhelmed this resilient community and threatened their sustainable way of life (e.g., destroyed pastureland and loss of livestock).

A way forward: Science for Sustainability and Safety:
There is therefore an important role for science to play in developing understanding of the interaction between geology, geography and changing climate on Tristan, to inform short and long-term mitigation strategies in response to anticipated localised impacts, and plan effectively for response to, and recovery from, future events. We need to understand the specific geological and hydrogeological context of the island in considerably more depth. Knowledge of recharge, storage and flow of groundwater in the volcanic edifice may help identify vulnerable locations for flooding and associated landslides, as well as strengthen water security.

This interdisciplinary study will include both research and policy components. The study will produce the first baseline hydrological and hydrogeological dataset recorded on Tristan; monitoring rainfall, runoff, storage, stream flow, groundwater levels and characterising recharge to produce a hydrogeological model of Tristan. As this work necessarily involves close interaction with the geology, we will gather further data (e.g., mapping; geochronology) to build on existing knowledge of the eruptive history and geomorphological evolution of the island. Collaboration with the local community and UK-based decision makers is essential. Much of the former will occur informally whilst working on the island over prolonged periods, although the research team can explore more formalised social scientific approaches to develop knowledge of how islanders interact with their changing environment. The latter will occur through a secondment with the project CASE partners, the UK Foreign and Commonwealth Office Overseas Territories Directorate, and engagement with other relevant government departments. This will support the move from a contributory/collaborative science-people-policy relationship to a more co-productive, citizen-led approach to maintaining monitoring and reporting of environmental change.

Research questions:
1) What are the mechanisms controlling surface water runoff, groundwater recharge, storage and flow on Tristan?
2) What are the actual or potential interrelationships between hydrogeological processes and geohazards on Tristan now and in the future? What comparisons can be made with other small active volcanic islands?
3) How can knowledge of geology, hydrogeology, and climate impacts support effective short and long-term mitigation strategies on Tristan, and by extension, other small volcanic islands?

Objectives:
a) Install hydrological/hydrogeological monitoring equipment on Tristan;
b) Gather and analyse the first ever baseline hydrological and hydrogeological dataset for Tristan;
c) Develop and validate the hydrogeological conceptual model of Tristan;
d) Conduct geological surveys to update maps;
e) Collect, prepare and analyse samples for stable water isotopic (18O/D) analysis;
f) Integrate knowledge and experience from secondment with CASE partner to develop context-appropriate outputs that are useable and useful for islanders and UK-based decision makers

Click on an image to expand

Image Captions

Aerial (drone) image of the only Settlement of Tristan da Cunha, the 1961-62 volcanic dome and flows to the left, the steeply rising snow-capped Peak, shallowing down to the Base, the sheer cliffs prone to mass movements, and the volcanic parasitic centres on the Settlement plain. Photo taken in 2022 by Neil Golding © Aquarius Survey & Mapping

Methodology

The aim of this research is to provide the first baseline hydrological and hydrogeological dataset recorded on Tristan in order to characterise surface and subsurface hydrological processes. This will necessitate understanding of the geology and geomorphological evolution of the island.

Desk-based review:
Desk-based review of existing knowledge and datasets (e.g., Baker et al., 1963, Dunkley, 1999, Hicks et al., 2012, 14, Hicks and Golding 2023) and remote sensing products to build an initial topographic and geological model, also drawing on comparisons with analogous small volcanic islands. This will be used to refine the monitoring and fieldwork plan.

Surface water and groundwater monitoring, sampling and measuring:
Surface and groundwater monitoring equipment will be installed during the first field campaign.

Surface water monitoring will include:
1) the installation of a weather station at the Settlement (just above sea-level) and on the mountain (between 1 km-2 km elevation), including a tipping bucket rain gauge, storage rain gauge, anemometer, and light meter;
2) the installation of water level gauges on priority rivers above the Settlement, and conducting stream gauging whilst the student is in the field at different flow rates where possible;
3) Grab sampling for stable isotope analysis (δ18O, δ2H) from surface water bodies (streams, lakes, storage rain gauges) and groundwater at fortnightly intervals (by the student and a trained local volunteer);
4) in-situ measurement of conductivity during grab sampling visits.

Groundwater monitoring will include:
1) the installation of level loggers (possibly multiparameter probes with temperature and conductivity) in existing boreholes/wells/springs. Dyke/spring mapping. Stable isotopes collected at same frequency as the surface water samples (to help characterise groundwater recharge). Depending on availability and/or ability to transport kit to the island, geophysical monitoring, piezometer drilling and pump testing could also be conducted.

Geological characterisation:
Ground-truthing and updating geological and volcanic feature maps, in-situ sample characterisation and collection for analysis. Possible specific sampling for 40Ar/39Ar analysis and possible further sampling of soils from ephemeral stream beds. Drone mapping if necessary.

Conceptual model development:
Using existing and new datasets, the student will create an updated geological model and the first hydrogeological model of Tristan. Surface and groundwater data will help develop understanding of water balances, particularly how important surface runoff is compared to groundwater. Groundwater data will contribute to understanding of aquifer properties. Results from isotope analysis will provide knowledge of recharge processes, sources and water ages using simple mixing models.

Current/future hazard assessment and mitigation options:
The student will combine the understanding of physical hydrological and volcanic processes developed through the conceptual model, with understanding of community vulnerability and resilience, to investigate different hazard scenarios and potential mitigation options. This will likely include some social science fieldwork with the local community to understand the dynamics of societal vulnerability to geohazards and perceptions of water security.

Connecting with the community:
This is an important aspect of the research process. It is anticipated that the PhD researcher will engage with the community regularly to share their research ideas, approaches, and findings. They will formally present their research at a community Town Hall meeting and for the Island Council. The student will be encouraged to integrate into community life, and contribute where appropriate, particularly sharing skills which may be beneficial (e.g., teaching).

It is essential that the student develops context-appropriate research outputs. The student and supervisory team will explore the use of virtual reality (VR) to support connectivity between the research problems and the community as well as provide exposure for the island, bringing wider attention to the opportunities and challenges of living and working on Tristan.

Project Timeline

Year 1

• Fieldwork to Tristan da Cunha. Possibly between Jan – Apr 2025. The priorities are installation of monitoring equipment and sample collection.
o Other important field-based activities include relationship development with community members and the Island Administrator, a presentation to the Island Council/community, and contributing to community life (e.g., farming, fishing, teaching students).
• Secondment (tbc) at the Foreign and Commonwealth Office (London or East Kilbride)
• Sample preparation at BGS, Lyell (HWU), and/or NEIF labs
• IAPETUS DTP training
• meetings with potential stakeholders, e.g., members of the Foreign and Commonwealth Office Overseas Territories Directorate, Ministry of Defence, Cabinet Office, to discuss research.
• Engagement with islanders charged with checking monitoring equipment, remote troubleshooting as necessary.

Year 2

• Return field visit to Tristan, either on the annual SA Agulhas (Sept – Dec 2025), or later in the austral summer (Jan – Apr 2026).
• Data analysis and output development
• Further sample preparation (if necessary) and sample analysis (incl. lab training)
• Secondment (tbc) at the Foreign and Commonwealth Office (London or East Kilbride)
• IAPETUS DTP training
• Presentation at an appropriate national conference (e.g., Volcanic & Magmatic Studies Group, EGU)
• Continued engagement with islanders and other stakeholders

Year 3

(Depending on field visit arrangements in Years 1 and 2, it is possible the second visit may occur in Year 3)
• Presentation of research at an appropriate international conference (e.g., International Association for Volcanology and Chemistry of the Earth’s Interior, Cities on Volcanoes, International Association of Hydrogeologists annual congress, EGU, AGU)
• Presentation of research approach and findings with CASE partners (e.g., via scenario exercises)

Year 3.5

• Finalisation and submission of the thesis.
• Development of academic papers
• Presentation of results at appropriate fora

Training
& Skills

The candidate will have a background in hydrology, hydrogeology, geology and environmental science. Interests or experience in civil and environmental engineering and applied social science is desirable.

It is essential that the candidate has the following skills:
• Strong ability in the field (physically fit and strong, able to hike long distances, unafraid of heights)
• Curious to work across disciplines (mainly physical and social sciences)
• Genuine desire to contribute to the community-and understand their way of life, cultural norms etc.

Training will be provided in the following areas (as necessary):
• Social scientific approaches to fieldwork and data analysis
• Mixed methods/interdisciplinary best practice training for geoscientists
• Hydrological and hydrogeological field methods, training for monitoring kit installation
• Sample preparation and analysis
• GPS field methods

References & further reading

Hicks et al., 2012 https://core.ac.uk/reader/9559710
Hicks et al., 2012 https://doi.org/10.1130/G33059.1
Hicks et al., 2014 https://doi.org/10.5194/nhess-14-1871-2014
Baker et al., 1963 http://doi.org/10.1098/rsta.1964.0011
Hicks and Golding (2023) is still embargoed but summaries can be emailed or found here: https://www.youtube.com/watch?v=yjMKvj1gaSk
Prada et al. 2016 https://doi.org/10.1016/j.jhydrol.2016.03.009

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